1. Field of Invention
This invention relates to a two-dimensional object position sensor usable to detect the position, orientation, size and/or location of an object.
2. Description of Related Art
The use of object position sensors is well known in the art. Typically, these sensors may include a light emitting diode placed in a fixed location that emits light energy in the direction of a photocell. When an object moves into the path of the light energy, the photocell ceases to send an electronic signal, thus indicating the presence of the object. Alternatively, the light emitting diode may be positioned to reflect light off of the object towards the photocell. In this arrangement, the presence of the would cause the photocell to generate an electronic signal.
In addition to these types of sensing devices, other sensing devices have been adapted for use in particular applications, such as photocopiers and printers. Typically, a sheet of paper is tracked as the sheet travels through the photocopier or printer using one-dimensional sensors or xe2x80x9cfax barsxe2x80x9d that detect the presence of the edge of a sheet of paper at a particular location within the photocopier or printer. These fax bars may use linear sensor arrays, which are only capable of sensing the object in one direction.
Small area imaging system such as CCD arrays and X-ray imaging systems have detector sizes on the order of 10 microns and 100 microns respectively. Due to the small pixel size and the technology that underlies the small area imaging arrays using such imaging arrays to sense the position of an object over a large area is impractical, especially when the object is in the near field of these small area imaging arrays.
Sensors usable to determine the size, position and/or location of objects are necessary in numerous operations and processes to allow for precise tracking and control of an object during the course of the process or operation. Typically, object position sensors may be placed in different locations along the path of an object undergoing a process. For instance, in an assembly line, object position sensors may be placed at various locations on the assembly line to indicate the presence of an object, such as a machine part in a manufacturing process. Object position sensors may also be used in package sorting operations involving a conveyor belt. In this type of operation, object position sensors may be placed at various locations along the conveyor belt to indicate the presence of an object, such as a box or package. In both the assembly line process and conveyor belt application, the object position sensors are used to track the progress of a box, package, or machine part through the process. This information may also be used to trigger other events within the operation or process itself.
Object position sensors are particularly applicable to photocopiers and printers to track and control the progress of a sheet of paper or other image recording medium as it progresses through the device. In conventional photocopiers and printers, a sheet of paper is tracked by a series of position sensors located at various points on a paper path within the device. In order for these position sensors to work effectively, the sheet of paper is constrained to have an edge placed along a side of the paper path, such that the object position sensor will positively register the presence of a sheet of paper. In addition, the sheet of paper may only positively be located within the paper path when it passes by one of these position sensors and is unaccounted at all other positions within the paper path. Because of this, it may often be difficult, for example, to pinpoint the exact location of a paper sheet that has become jammed in the paper path.
In such conventional photocopiers and printers, these position sensors are often only capable of sensing a sheet of paper in one dimension. A fax bar is one such device used in fax machines, copiers and printers which is capable of sensing the presence of a sheet of paper in only one dimension. While this type of sensing capability may be effective for tracking and controlling the motion of a sheet of paper in such conventional copiers and printers, the tracking and control capabilities of photocopiers and printers could benefit from providing an ability to handle a wide variety of sheet sizes and media types, multiple sheets moving together, to use center registration, and to position the sheets in arbitrary trajectories, that is, for example, by eliminating the constraint that the sheets have an edge positioned against the side of the paper path. Conventionally, if a paper path of a photocopier or printer were to be provided with such capabilities, a large number of discrete sensors would be required. While this may provide improved tracking of a sheet of paper throughout the paper path, it is an option that is currently uneconomical and impractical.
This invention provides systems and methods for sensing the size and position of an object with a two dimensional array of sensors that spans at least a portion of the path of the object.
This invention separately provides systems and methods that track an object continuously over a relatively long distance, such that the position of the object may be determined at any time while the object is in the vicinity of the array.
In various exemplary embodiments, the two-dimensional array of sensors may be fabricated inexpensively and may track an object with relatively high precision as it travels across a large area.
In various exemplary embodiments of the systems and methods according to this invention, an object position sensor uses a close-packed array of analog sensor elements, or pixels, along with appropriate illumination to determine object edge positions, and to infer object size, orientation, shape and position. In some exemplary embodiments, this is accomplished by distributing a series of light sources over the surface of a substrate such that light energy will be directed towards a series of discrete light energy detectors, or will reflect off of an object toward these discrete light energy detectors. In various exemplary embodiments, a collimating film is positioned over the light energy detectors to reduce the amount of low-angled light energy that reaches the surface of the light energy detectors. In some exemplary embodiments, a transmissive plate is positioned over the collimating film or over the analog sensor elements to allow an object to pass over the light energy detectors.
In various exemplary embodiments, the electrical signals from the sensors may then be locally digitized and hierarchically processed. In a reflective-type system, when an object, such as a sheet of paper, passes in the vicinity of the light energy detectors, light energy emitted from a light source is reflected off the surface of the object, passes through the collimating film, and is received by some of the light energy detectors. Alternatively, in a transmissive-type system, the light sources may be positioned opposite the light energy detectors. In this configuration, an object would block the light energy from reaching the light energy detectors.
In various exemplary embodiments, the sensor systems of this invention may be fabricated inexpensively using methods similar to those used to make large area solar cells or large area photoreceptor media, such as organic photoreceptor belts. These processes use roll-to-roll fabrication, which creates amorphous-Si:H photodiodes on a foil substrate, such as polyimide, or organic photoconductor on polyester. An organic photoreceptor sensor may be deposited on a substrate by a large-scale evaporation process, in the case of small molecule organics, or by a printing or coating process for polymer-based organics. In these exemplary embodiments, lateral patterning of the photosensitive material is not necessary. That is, the photo-responsive material is continuous and uniform. In this case, electron-hole pairs created by light absorbed in areas not containing collection electrodes simply recombine and do not drift to the collection electrodes. The lateral conductivity of the photosensitive material of these embodiments is low enough to essentially isolate the sensor elements.
The sensor elements of the sensor system can be arranged in arrays and have a relatively large size and/or pitch. For example, the center-to-center spacing or pitch can be sufficient to allow for sensors having a diameter of one cm in the case of a circular sensor element. Through the use of arrays, the position sensing resolution of the sensor systems and methods of this invention are considerably finer than the size and pitch of the sensor elements themselves. In this way, large areas may be covered by arrays of analog sensor elements to determine the position and size of an object in proximity to the array.
For instance, in a photocopier, these two-dimensional arrays of sensor elements may extend over the entire paper path, such that a sheet of paper can be continuously and accurately tracked throughout the entire process, including around the curves and bends of the paper path. Further, because the size and shape of the object may be determined through the use of the array of sensor elements, processes may be adapted to handle a wide variety of object sizes. For instance, the sensor systems and methods of this invention could be used in a photocopier to determine a variety of sheet sizes and media types, to determine if multiple sheets are moving together, to use center registration and to determine the position of a sheet of paper such that the photocopier may make adjustments or reposition the sheet of paper based on the information received from the position sensors.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.